Dissolved major ions, Sr and sup(87) Sr/ sup(86) Sr of coastal lakes from Larsemann hills, East Antarctica: Solute sources and chemical weathering in a polar environment

Abstract

Dissolved major ions, Sr concentrations and sup(87) Sr/ sup(86) Sr ratios of ten coastal lakes from the Larsemann Hills, East Antarctica have been studied to constrain their solute sources, transport and glacial weathering patterns in their catchments. In absence of perennial river/streams, lakes serve as only reliable archive to study land surface processes in these low-temperature regions. The lake water chemistry is mostly Na-Cl type and it does not show any significant depth variations. Sr isotope compositions of these lakes vary from 0.7110 to 0.7211 with an average value of 0.7145, which is higher than modern seawater value. In addition to oceanic sources, major ions and Sr isotopic data show the appreciable amount of solute supply from chemical weathering of silicate rocks in lake catchments and dissolution of Ca-Mg rich salts produced during the freezing of seawaters. The role of sulphide oxidation and carbonate weathering are to be found minimal on lake hydro-chemistry in this part of Antarctica. Inverse model calculations using this chemical dataset provide first-order estimates of dissolved cations and Sr; they are mostly derived from oceanic (seawater + snow) sources (cations approx. 76 percent) and Sr approx. 92 percent)) with minimal supplies from weathering of silicates (cations approx. 15 percent); (Sr approx. 2 percent) and Ca-rich minerals (cations approx. 9 percent); Sr approx. 7 percent). The silicate weathering rate and its corresponding atmospheric CO sub(2) consumption rate estimates for Scandrett lake catchment (3.6 plus or minus 0.3 tons/km sup(2)/yr and 0.5 x 10 sup(5) moles/km sup(2)/yr), are lower than that of reported values for the average global river basins (5.4 tons/km sup(2)/yr and 0.9 x 105 tons/km sup(2)/yr) respectively. The present study provides a comprehensive report of chemical weathering intensity and its role in atmospheric CO sub(2) consumption in low-temperature pristine environment of Antarctica. These estimates underscore the importance of Antarctica weathering on atmospheric CO sub(2) budget, particularly during the past warmer periods when the large area was exposed and available for intense chemical weathering.